I have tried all the plugs u mentioned, Denso irridium, NGK Paltinum, NGK double platinum, Bosch platinum, HKS, Apexi , Bosch super 4, Brisk 360 degree etc. I can confess the best, value/performance -for-money, still Bosch super 4. Others, like irridium is prone to misfire once the ground electrode worn out, even at a very small one.
U don't have to waste ur money like what I did, in the name of curiosity. Till today, after 5 years, my super 4 still serving my engine well. All u need to do is to clean ur plugs using a fine wire brush, and have them installed back. By the way I still have those expensive exotic metal plugs clean & kept nicely in frame. Interested?, may be I can send them to gold smith to make them into locket jewelry...he...he